Method of retarding deposition of coke in petroleum furnaces



United States Patent 3,170,865 METHOD OF RETARDHNG DEPOSITION 0F COKE INPET'RQLEUM FURNAES James E. Allen, Houston, and Douglas K. Layne,Arlington, Tern, assignors to Dow Corning Corporation, Midland, Mich, acorporation of Michigan No Drawing. Filed July 17, 1961, Ser. No.124,353 3 (Ilaims. (Cl. 208-48) One of the continuing problems in thepetroleum refining industry is the deposition of coke in furnaces wherethe petroleum is heated to temperatures above the cracking temperatureof that material. This is done in many phases in the refining andpreparation of petroleum products.

Usually the furnaces employed for heating the petroleum are tubefurnaces in which the petroleum passes through a series of tubes, whichtubes are heated to temperatures of 500 to 1000 F. At this temperaturethe petroleum cracks, but is maintained in liquid form by the hightemperature and high pressures employed. The liquid product then passesout of the tube furnace into a second stage where it may be eitherallowed to solidify as in the case of coke preparation, or it may beburned as in the preparation of carbon black, or the liquid may be putthrough some other process.

The problem which has heretofore been unsolved has been that in spite ofthe high temperature and pressure employed in the tube furnaces, therewas a deposition of solid carbonaceous material on the walls of thetubes. This deposition continues at a suflicient rate so that itseriously interferes with the flow of petroleum through the furnace. Infact, often the deposition was so rapid that the furnace would have tobe shutdown after 30 days operation, or at the most after three monthsoperation in order to clean out the tubes. Most of the time thedeposition of the coke was so severe that it was cheaper to merelyreplace the tubes rather than clean them out.

Furthermore, the deposition of coke in the tube reduces the rate of flowof the petroleum, thereby subjecting it to the extremely hightemperatures for longer than the desired time. This tends to increasethe rate of deposition of the coke and thereby complicated the problem.In addition, the deposition of coke introduced a hazard due to theweakening of the tube walls.

Applicants have found unexpectedly that this deposition of coke inpetroleum furnaces can be prevented, or greatly retarded by mixing withthe petroleum prior to introduction into the furnace from .1 to 100parts per million of a methylpolysiloxane, in fluid form, based upon theweight of the petroleum.

The siloxane can be introduced into the petroleum at any time prior topassage through the furnace. Furthermore, the siloxane can be mixed withthe petroleum in any convenient manner. The preferred method is todilute the silxone with an inert solvent, such as a hydrocarbon solvent.In general, the preferred concentration is from one part siloxane to 30parts solvent to one part silxone per 50 parts solvent. The siloxane isintroduced continuously into the petroleum, however, the rate ofintroduction need not be constant. In other words, during the initialpart of an operation one may introduce the siloXane at the rate of partsper million based on the weight of the petroleum while during the latterpart of an operation one may reduce the siloxane to 3 parts per million.

Any methylsiloxane which is in fluid form can be employed in thisinvention. The term in fluid form" means that the siloxane can be eithera fluid per se at room temperature or it has been rendered fluid by theintroduction of a solvent. The term methylsiloxane includes thosepolysiloxanes in which all of the hydrocarbon substituents on thesilicon are methyl radicals and it also includes those siloxanes inwhich some of the substituents are methyl radicals, whereas the othersubstituents are hydrogen, or hydrocarbon radicals such as ethyl,phenyl, B-phenylpropyl, fl-phenylethyl, or vinyl.

The physical structure of the siloxane is immaterial so long as it is influid form. Thus the viscosity of the siloxane can range from less thanone cs. to non-flowing gums. Furthermore, it is immaterial whether thesiloxane has terminal organic groups or terminal hydroxyl groups orwhether it is linear, cyclic or branched in molecular configuration.

The following examples are illustrative only and should not be construedas limiting the invention which is properly delineated in the appendedclaims.

Example 1 This example illustrates the utility of the method of thisinvention to prevent coke buildup in a coking furnace employingpetroleum residium.

The petroleum residium was passed through a pipe line into a cokingfurnace where it was heated to a temperature of 900 F. The moltenresidium was then passed through a second line into a cooling tank wherethe coke was allowed to solidify. During operation of the apparatus adimethylpolysiloxane of 12,500 cs. was introduced into the petroleumresidium prior to passage through the cracking furnace at a rate of 10parts per million. The siloxane was introduced continuously bydissolving it in kerosene to a concentration of one part of siloxane to50 parts kersene and then pumping the solution into the petroleum lineat a suificient rate to give the desired concentration of siloxane inthe petroleum residium.

The furnace operated for 8 months without any shutdown due to thedeposition of coke in the tubes. When the apparatus Was operated withoutemploying the siloxane the furnace had to be shutdown at least aboutevery three months for the cleaning or replacement of the tubes.

Example 2 Equivalent results are obtained when petroleum is passedthrough a vaporizer furnace and heated at a temperature of 900 F. andthe effluent gases thereafter burned to form carbon black.

Example 3 Equivalent results are obtained when the following siloxanesare employed in the process of Example 1:

That which is claimed is: l. A method of extending the furnace life inpetroleum furnaces by preventing, or decreasing coke accumulation in thefurnace which comprises mixing with the petroleum prior to heating inthe furnace from .1 to 100 parts per million of a polyrnethylsiloxane influid form, based on the weight of the petroleum.

2. The method of claim 1 in which the silox-ane is apolydimethylsiloxane.

3. A method of extending the furnace life of petroleum tube furnaces bypreventing or decreasing coke accumulation in the furnace whichcomprises mixing with the petroleum prior to heating in the furnace from.1 to 100 parts per million of a polymethylsiloxane in fluid form, basedon the weight of the petroleum.

References Cited by the Examiner UNITED STATES PATENTS 2,908,624 10/59Johnson et a1. 208-48 2,968,616 1/61 Bernard 260-4482 OTHER REFERENCESSilicones, New Tools for Petroleum Operations, F. L. Resin, Oil and GasJournal, Aug. 2, 1954, page R-1l15.

10 ALPHONSO D. SULLIVAN, Primary Examiner.

MILTON STERMAN, Examiner.

1. A METHOD OF EXTENDING THE FURNACE LIFE IN PETROLEUM FURNACES BYPREVENTING, OR DECREASING COKE ACCUMULATION IN THE FURNACE WHICHCOMPRISES MIXING WITH THE PETROLEUM PRIOR TO HEATING IN THE FURNACE FROM.1 TO 100 PARTS PER MILLION OF A POLYMETHYLSILOXANE IN FLUID FORM, BASEDON THE WEIGHT OF THE PETROLEUM.